Industrial bags, often made from multi-ply kraft paper, synthetic sheets, and combinations thereof, are closed in numerous ways. A common closure is referred to as a pinch bottom where a flap of one wall of the bag is folded over and glued or otherwise secured to another wall of the bag. The pinch bottom closure is commonly used in gusseted bags and flat tube bags.
Once closed it becomes necessary at some point to open the bag. In bags that were sewn shut, it is possible to open the bag by undoing the stitching. Sewing generally requires substantial additional processing equipment and processing expense, and thus is no longer a preferred closure method. Providing a glued closure for a pinch bottom bag provides for an easily automated process that is inexpensive and yields a secure sift resistant closure. However, glued closures are difficult to open without cutting the bag, or substantially tearing the walls of the bag. The walls of the bag, of course, are designed to resist tearing, which further makes opening of the bag difficult, and cutting requires having a cutting tool to be handy.
In U.S. Pat. No. 4,480,752 there is disclosed a feature for a pinch bottom bag that facilitates the opening of the bag. The feature includes a tab which is bonded inside the bag within one of the side wall gusset folds. A portion of the tab extends out of the interior of the bag and as the bag is folded closed, remains exposed to the exterior of the bag. By pulling on the tab, the pinch bottom closure is opened in an area surrounding the tab.
In commonly-assigned U.S. patent application Ser. No. 08/768,389, the disclosure of which is hereby expressly incorporated herein by reference, an easy opening feature for industrial bags is also described. A tab is bonded into the bag with a portion extending outwardly from the bag, and the side walls of the bag are formed to include at least one tear line to cause localized tearing of the bag during opening as well as to reduce the effort required to open the bag. In particular embodiments of the bag, tear lines may be formed in both the front and back walls of the bag and arranged so as to align and overlap in a double fold closure.
Disposing the tab within the bag may cause difficulty when the bag is used for particular contents materials. For example, if the bag is to contain pet food, the pet food will typically have a desired fat content. Unless the tab is specially treated, such as coated with silicon or formed from synthetic materials, over time the tab will wick fatty oils from the pet food to the exterior of the bag. The fatty oils make the tab difficult to grasp hindering opening of the bag, may weaken the tab causing it to fail as the bag is opened, may distort printing disposed on the bag and/or the tab, and may further attract insects and rodents. Using silicon coated tabs and or synthetic materials to form the tab presents problems in effectively gluing the bag closed.